Serum levels of parathyroid hormone and markers of bone metabolism in patients with rheumatoid arthritis. Relationship to disease activity and glucocorticoid treatment.

OBJECTIVE

To evaluate the influence of inflammatory activity and glucocorticoid (GC) treatment on serum parathyroid hormone (s-PTH) and bone metabolism in patients with rheumatoid arthritis (RA). Furthermore, in patients with active RA, to examine the PTH secretion and Ca2+ set point before and after treatment with GC.

METHODS

A range of biochemical markers of bone metabolism and calcium homeostasis were measured in 95 patients with definite RA stratified into groups according to disease activity and GC treatment. In a subgroup of 12 patients with active disease, initiating slow-acting-anti-rheumatic-drugs (SAARDs) +/- GC, the PTH secretion and calcium set point were evaluated by use of the Cica clamp technique before and after 1 month of treatment.

RESULTS

S-osteocalcin, s-total alkaline phosphatase (s-TAP) and s-carboxyterminal cross-linked telopeptide of type I collagen (s-ICTP) were elevated in all groups. The levels of urine pyridinoline (Pyr) and s-albumin-corrected calcium (s-AlbCorrCa2+) were elevated in patients with active disease and patients treated with GC. S-PTH and s-phosphate were within normal ranges. S-TAP, s-ICTP, Pyr and s-AlbCorrCa2+ correlated positively with indices of disease activity. In the subgroups undergoing the Cica clamp technique, no difference in PTH responsiveness of B-Ca2+ was unveiled.

CONCLUSIONS

Neither active disease nor GC therapy appears to induce secondary hyperparathyroidism, nor is there an alteration in PTH responsiveness of B-Ca2+ in patients with RA. The increased levels of markers of type I collagen metabolism (s-ICTP, Pyr) and s-AlbCorrCa2+ in patients with active disease and patients treated with GC may be a result of increased degradation in synovium, cartilage and bone due to the inflammatory process.